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In this paper, we conducted photoluminescence (PL) and time-resolved photoluminescence (TRPL) measurements for the organic films that was composed of tris(8-hydroxyquinoline) aluminum (Alq 3 ) as the host and 10-(2-benzothiazolyl)-1, 1, 7, 7-tetramethyl-2, 3, 6, 7-tetrahydro-1H, 5H, 11H, [l] benzo-pyrano [6,7,8-ij] quinolizin-11-one (C545T) as the green dopant with different concentration. Typical quench behavior was observed by typical PL measurements when doping concentration exceeds 2% and the carrier lifetime decreased monotonically with increasing doping concentration in TRPL measurements. Time constant for energy transfer from host to dopant decreased with increasing dopant concentration and saturated above 2% dopant concentration. An anomalous blue shift at the initial probe time-interval was observed when dopant concentration was over 4%. It indicated a fast event energy absorption and/or relaxation process which had a time constant less than two picosecond. Two physical mechanisms with different time constant was observed those accounted for the concentration quench behaviors in the Alq3/C545T system.

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In this paper, we study device performance and carrier dynamics of an organic light-emitting device (OLED) with an emitting layer (EML) based on a mixed-host (MH) structure. Such a structure is composed of two different host and one dopant materials. It exhibits longer operation lifetime as compared with a conventional heterojunction (HJ) device. In such a MH layer structure, carrier transport characteristic is modified and emission zone position is changed. Energy transfer from the two hosts to one dopant is studied by EL, PL and TRPL measurements. We observe spectrum shift from the EL measurement under different current injection. Incompletely energy transfer from NPB to DPAVBi is shown in cw PL measurement. Time constant at different probe wavelengths with different mixing concentration suggests that different energy transfer in such a MH structure.